We propose to develop Listeria monocytogenes, as a cancer therapeutic for HER-2/neu expressing breast tumors. We have shown that recombinant L. monocytogenes that secretes a tumor specific antigen can not only protect against tumor challenge but can also induce regression of macroscopic established tumors after transplantation into normal syngeneic mice. This impressive anti-tumor response is probably due to the unusual ability of this facultative intracellular bacterium to escape the phagolysosome and live and grow in the cytoplasm of cells. Antigens secreted by L. monocytogenes, therefore, are very effectively targeted to both the class II and class I restricted pathways for antigen presentation. Thus this bacterium may be the ideal vaccine vector for boosting the cell mediated immune response to tumor specific antigens as a cancer therapeutic. To determine how to optimize the use of L. monocytogenes as a cancer vaccine in humans we will use a HER-2/neu transgenic mouse model of breast cancer on the FVB background to test the ability of L. monocytogenes to overcome tolerance to spontaneously arising tumors. Since the first submission of this grant we have completed the construction of Lm vectors rquired to perform these experiments, including five Lm-LLO-Her-2/neu strains that secrete overalpping fragments of the HER-2 protein and discovered that they appear to reveal cryptic epitopes in HER-2/neu when delivered to the normal and HER-2/neu transgenic FVB mouse. We have verified that these epitopes are revealed by fusing the antigen to LLO and delivery by L. monocytogenes and not by delivering HER-2/neu as protein fragments.Thus a new sub- aim of this proposal (Specific Aim 1c) is to fully map these epitopes so that we can measure their contribution to the overall immune response in Specific Aim 2. The goal of Specific Aim 2 is to correlate the anti-tumor effectiveness of the Lm-LLO-HER-2/neu recombinants with the induction of B and T cell immunity. Finally, in Specific Aim 3, we will compare the efficacy of the Listeria HER-2/neu vaccines to impact on transplanted and spontaneously arising breast tumors in mice transgenic for HER-2/neu. Since the last submission we have found that the five Lm-LLO-Her-2/neu fragment vectors have different abilities to impact on sponataneous tumor growth but have similar impacts on the tranplantable tumor in the HER-2/neu trangenic mouse and have added new aims that explore the mechanism behind this finding.